The current trend for many mining operations is the use of large hydraulically operated front loading shovels for loading large off road trucks. One of the problems encountered with designing and manufacturing such shovels is the availability of hydraulic components sized to handle the required hydraulic flow. For example, the hydraulic systems for smaller front loading shovels and similarly sized hydraulic excavators typically have a pair of three spool valve assemblies connected to a center manifold to provide a parallel flow arrangement to the hydraulic motors. However, the physical size of the valve bodies of the valve assemblies needed for larger front loading shovels is such that specialized manufacturing equipment, i.e., both foundry equipment for casting the body and precision machining tooling for machining the castings would have to be acquired to make the valves. Since the demand for such large shovels is not expected to match, for example, the demand for smaller vehicles, the cost of the specialized equipment would have to be amortized over a smaller number of vehicles thereby making the cost of the hydraulic system way out of line with the cost of the total vehicle.
Another example would be the availability and/or cost of the hydraulic pumps if a single hydraulic pump were used for providing total flow for the hydraulic system. Typically, a variable displacement hydraulic pump having a displacement of 1000 lpm would cost more than twice that of a hydraulic pump having a displacement of 500 lpm.
Accordingly, in view of the above, it would be desirable to be able to use multiples of existing smaller valve assemblies in such a way to provide a hydraulic system for a large vehicle having the desired fluid flow handling capability. Using multiples of existing smaller valve assemblies will reduce the overall vehicle cost in several ways. For example, a single large valve costs more than two smaller valves having a combined flow capacity of the larger valve. Moreover, using existing valves minimizes the development cost that would be required to design, build and test a new larger valve.
The present invention is directed to overcoming one or more of the problems as set forth above.